Cehmical manufacture



Patented May 18, 1943 @WGAL MANUFACTURE .lames Douglas Macltlahon, Niagara Falls, N. it

tumor to The Mathieson Alkali Won-ha, 1nd,,

New York, N. Y a corporation or Virginia No Drawing. Application lune 24, 1039, Serial No acacia h purit is used, there is apparently sufllcient This invention relates to an improved calcium hypochlorite product which produces a clear solution when dissolved in water containing carbonate and bicarbonate ions.

In the use of solutions containing calcium ions and hypochlorite ions, it has been observed that when certain natural waters are used as solvents, a turbidity or very fine white granular suspension is gradually formed in the solution, although at the start the solution may have been clear. This presents a serious disadvantage to the use of calcium hypochlorite solutions, particularly when used as sterilizing solutions. The formation of this fine white suspension is particularly disadvantageous since the finely divided granular precipitate formed tends to adhere to surfaces exposed to the solution. For example, in the dairy industry, a particularly advantageous mixture used for sterilizing purposes consists of calcium hypochlorite of high purity admixed with a salt such as sodium chloride. When a product such as this is dissolved in certain natural waters, the formation of a finely divided precipitate which adheres to the surfaces of the equipment being sterilized is particularly objectionable. Generally speaking, solutions containing calcium ions and hypochlorite ions which are used for such purposes are initially clear when the hypochlorite used is of high quality and when it is used in an amount such that the concentration of available chlorine does not exceed about 300 parts per million. When higher concentrations are employed or when a hypochlorite product of lesser purity is used the initial solutions wil loften possess a certain degree of turbidity. In the first case where the solutions are initially clear the objectionable fine white precipitate slowly de velops causing turbidity, and in cases where the solution is originally turbid, the turbidity is considerably increased when the referred to natural waters are employed.

The formation of this finely divided white pre-- ions which cause a finely divided CaCOa to precipitate. The following equation indicates the probable course of such a reaction:

Even though a. calcium hypochlorlte of relatively to hydroxyl ion concentration to cause the formation of this objectionable precipitate according to the above equation.

I have found that the above dimculties can be overcome by employing a mixture containing, in addition to the calcium hypochlorite product, a relatively mall amount oi sodium tetra phosphate (NarPrOrs) This tetra phosphate is solubio in water in intimate association therewith. The solution resulting ircm dissolving such a mixture in water. even though the water may be high in temporary hardness, retains its original clarity for long mriods or time, or it originally turbid does not increase in turbidity.

The calcium hypochlorite which I prefer to use as the primary constituent in the product of the present invention is one which is a stable product i ch in available chlorine and low in calcium chloride and calcium hydroxide. The calcium hypochlorite prmuct the preparation of which is described in United States Letters Patent No. 1,7810%, granted to Robert B. MacMullin and Maurice C. Taylor on an application filed August 16, 1928, is particularly useful in the product of the present invention. In general, it is advantageous to use a calcium hypochlorite containing upwards of available chlorine, or better upwards of available chlorine, and not more than about 10% of calcium chloride and a minimum of free lime. The invention is, however, also useful when embodied in mixtures the primary constituent of which is conventional bleaching powder or chlorinated lime, since the admixed tetra phosphate does not impair the sta- :bility of such products as would sodium carbonate, for example. Bleaching powder or chlorinated lime is not. strictly, a calcium hypochlorite but it does form a solution in water containing calcium ions and hypochlorite ions.

I have found that the addition of sodium tetra phosphate to calcium hypochlorlte compounds of the type described in proportion as low as 1 part to 14,000 parts of the hypochlorite will efiectively revent turbidity in water solutions to which a quantity of the mixture sufficient to produce an available chlorine concentration below "300 parts per million has been added. In the preparation of the dry product of the present invention, however, I prefer to employ quantities of the soluble tetra phosphate not less than about 0.5 or 1 part per parts of the hypochlorlte. This is a practical expedient occasioned by the physical dimculties involved in properly mixing the dry salts when a lower proportion of the tetra phosphate is used. The iineness or division or the salts themselves as well as the eiilciencies oi. the mixing devices are considerations in this problem. For highest eiliciencies it is, therefore, recommended that quantities or tetra phosphate within the range 0.5-20 parts to 100 parts of the hypochlorite be used. I have round that mixtures containing proportions of sodium tetra phosphate higher than about 20 parts to 100 parts oi the hypochlorite have an increasing tendency to produce a heavy, well flocculated precipitate. In general, quantities or the tetra phosphate between 1 and 3 parts per 100 parts of the hypochlorite produce maximum emciencies when the mixture is later dissolved in water containing temporary hardness. With increasing efllciency or mixing, the lower limit moves down.

The mixture or this invention may also include inert diluent salts such as sodium chloride added to keep the available chlorine content of the total composite mixture within some desired maximum limit, a available chlorine limit, for example. Such a mixture may comprise 13 parts or the hypochlorite, 86 parts of common salt and 1 part 01' tetra phosphate for example. The physical dimculties involved in proper mixing noted above may require the use of somewhat increased proportions of tetra phosphate in such mixtures unless the tetra phosphate is incorporated into the hypochlorite before the salt is added to the mixture.

I am unable to give a complete explanation of the manner in which the improved product of my invention operates when placed in solution, either to prevent precipitation or to so completely disperse the CaCOa that the resulting solution appears to be clear. It will be noted that the quantity oi tetra phosphate used is but a small fractional part 01' the stoichiometrical equivalent of the calcium ion present, so that the possibility of any stoichiometrical reaction with the calcium ion such as, for example, the formation of soluble compounds containing a complex ion of calcium and tetra phosphate would appear to be eliminated. As a hypothesis I suggest that the results obtained may be due to a peptizing effect caused by a complex tetra phosphate ion associating itself with a calcium carbonate particle of colloidal dimensions. It is to be understood, however, that my invention is not in any way predicated on such a theory of the mechanism of the reaction occurring in the solution which results from dissolving the herein described product in water containing temporary hardness.

I claim:

1. An improved product for forming aqueous solutions containing calcium ions and hypochlorite ions, comprising a calcium hypochlorite and, in intimate association therewith, sodium tetra phosphate in proportion approximating 0.5%,- by weight on the calcium hypochlorite.

2. An improved product for forming aqueous solutions containing calcium ions and hypochlorite ions, comprising a calcium hypochlorite and, in intimate association therewith, sodium tetra phosphate in proportion approximating 0.5%- 20% by weight on the calcium hypochlorite, and an inert diluent salt.

3. An improved product for forming aqueous solutions containing calcium ions and hypochlorite ions, comprising a calcium hypochlorte containing upwards 01 available chlorine and, in intimate association therewith, sodium tetra phosphate in proportion approximating 0.5%-20% by weight on the calcium hypochlorite.

4. An improved product for forming aqueous solutions containing calcium ions and hypochlorite ions. comprising a calcium hypochlorite containing upwards oi. 50% available chlorine and, in intimate association therewith, sodium tetra phosphate in proportion approximating 0.5%- 20% by weight on the calcium hypochlorite, and an inert diluent salt. 7

5. An improved product for forming aqueous solutions containing calcium ions and hypochlorite ions, comprising a chlorinated lime, and in intimate association therewith, sodium tetra phosphate in proportion approximating 0.5%- 20% by weight on the chlorinated lime. 6. An improved product for forming aqueous solutions containing calcium ions and hypochlorite ions, comprising a calcium hypochlorite and, in intimate association therewith, a water soluble tetra phosphate in proportion approximating l%-3% by weight on the calcium hypochlorite.

7. An improved product for forming aqueous solutions containing calcium ions and hypochlorite ions, comprising a calcium hypochlorite and, in intimate association therewith, a water soluble tetra phosphate in proportion approximating 0.5 %-20% by weight on the calcium hypochlorite.

8. An improved product for forming aqueous solutions containing calcium ions and hypochlorite ions, comprising a calcium hypochlorite and, in intimate association therewith, a water soluble tetra phosphate in proportion approximating 0.5%-20% by weight on the calcium hypochlorite, and an inert diluent salt.

9. An improved product for forming aqueous solutions containing calcium ions and hypochlorite ions, comprising a calcium hypochlorite and, in intimate association therewith, a water soluble tetra phosphate in proportion approximating l%3% by weight on the calcium hypochlorite, and an inert diluent salt'.

10. A dry composition containing calcium hypochlorite and from about 0.5% to about 10% of sodium tetraphosphate.

JAMES DOUGLAS MACMAHON. 

